It sounds for sure, from your saying top line is dark and 2nd line is light, that you are failing to initialize the LCD display controller correctly. I have seen this behaviour a number of times. Also note that you should check closely at which controller chip is used on the LCD module. There are several different families of parts in the industry that are in use. Some are exact clones of the "original" Hitachi chip, which is the most common, whilest others exhibit different operational details. I recently had a client that switched sources on an 8x2 LCD display that they were using in production only for them to "discover" that the display showed stray characters on the screen at power up until the 8051 software got around to clearing the module and painting the first screen.